Ziegler-Natta (Z-N) and metallocene-alumoxane type catalyst systems for the polymerization of olefins are well known in the art. Recently a new, ionic pair type of catalyst has been developed which yields polymers of improved properties compared to those made with conventional catalyst systems.
These systems typically use Group IV-B metallocene catalysts prepared as a reaction product of a Group IV-B metal metallocene compound and an ionic activator compound. U.S. Pat. No. 5,241,025 teaches the use of a catalyst system comprising a Group III-A element compound comprising a cation capable of donating a proton which will irreversibly react with at least one ligand contained in the Group IV-B metal compound and an anion which is bulky, labile and non-coordinatable with the Group IV transition metal cation produced upon the reaction of the metallocene and activator compound. Similarly, U.S. Pat. No. 5,198,401 teaches that ionic catalyst compositions can be prepared by combining two components, bis(cyclopentadieny) Group IV-B metal complex containing at least one ligand which will combine irreversibly with the second component or at least a portion thereof such as a cation portion thereof. The combination of the two components produces an ionic catalyst composition comprising a cationic bis(cyclopentadienyl) Group IV-B metal complex which has a formal coordination number 3 and a 4+ valence charge and the aforementioned non-coordinating anion. Both of these U.S. patents are directed to homogenous metallocene polyolefin catalyst systems. Use of these catalyst systems in other reactor designs, particularly slurry reactors, can result in reactor fouling, poor productivities, poor polymer bulk densities, and poor polymer particle morphologies. For these reasons, it is desirable to develop heterogeneous versions of these ion pair cocatalysts, where the cocatalyst is deposited on a carrier, preferably an oxide such as silica or alumina.
An example of a supported ion pair catalyst system is taught in WO 94/03506, wherein a support which had been modified with an alkyl aluminum reagent is treated with a solution of a metallocene catalyst and an anionic activator, and the solvent is removed. The resulting catalyst system provided a low activity heterogeneous ion pair catalyst system. Because there is no direct chemical bond between the catalyst ion pair and the support, resolubilization of the catalyst may make this system unsuitable for slurry reactors.
WO 93/11172 discloses the use of certain polyanionic transition metal catalyst compositions wherein the polyanionic moiety comprises a plurality of metal or metalloid atoms--containing non-coordinating anionic groups pendant from and chemically bonded to a core component through use of a carbon containing a spacer between the metal or metalloid atoms and the core component. However, WO 93/11172 teaches to avoid exposing its activator to high concentrations of functionalities which are known poison for metallocene polymerization catalysts and in fact, teaches the necessity of masking reactive functionalities on a support, such as hydroxyl-groups on silica.
The present invention overcomes the above mentioned problems and provides further improvements to catalytic systems by providing a catalyst activator chemically bound directly to the support, reducing resolubilization of heterogenous catalysts and therefore minimizing reactor fouling. Furthermore, the present invention further permits the use of supports having high concentrations of chemical functionalities that would otherwise act as poisons to metallocene catalysts.
In addition, the direct bond between the support and the catalyst activator provides a large support effect, allowing properties of the activator to be altered by modifying the support and consequently, permitting the support to influence the polymer morphology.
Furthermore, catalyst systems containing the present activator produce a high bulk density polyethylene. The high bulk products cost less to ship to end users, flow better in molding operations and eliminates the need to pelletize what would otherwise have been a resin fluff.
Additionally, multi-modal polyolefin resins may be prepared using the supported catalytic activator of the present invention with a mixture of catalysts, including chromium, Ziegler-Natta and metallocene catalysts.